Indoor air pollution is a problem that is receiving much attention. Particulates in the air cause multiple problems, and include deposition of particulate matter in the airways, inhalation of toxic chemicals, metals and fibers that are present in the air, and exacerbation of allergic reactions in humans and animals. The presence of improperly maintained upholstery and carpets in confined spaces adds to the transmission and retention of particulates and allergens.
An allergen is a substance that causes an allergic reaction in an human or animal who is exposed to the substance. A comprehensive list of allergens is not possible, because sensitivities vary from person to person and it is possible for someone or an animal to be allergic to almost any substance.
A growing issue for children and adults is the increase in allergic asthma. In recent years, numerous hypotheses have advanced the biological plausibility for the exacerbation of allergic asthma likely associated with episodic exposure to allergens bound to soil particles, transported to lower tracheobronchial (TB) and alveolar (A) regions of the lung. Typically, allergens such as dander, including house mite, cockroach, cat, or dog allergens, or pollens such as ragweed, rye grass, or pine are found mainly in the coarse fraction of airborne particles. However, allergens can also be found in respirable particles that differ in particle size and chemical composition.
Recent studies show that all types of particles appear to exert an adjuvant effect on the immune response to co-administered protein antigen, indicating that inhaled antigen in particle-exposed individuals plays a major role in allergic asthma. Different particles stimulated distinct types of immune responses. Studies suggest that particles could modulate airway disease through their actions on airway epithelial cells and that bronchial epithelial cells from asthmatics are different from those of non-asthmatics.
Evidence also suggests that metals commonly found in particulate matter are responsible for augmentation of allergic sensitization and may be responsible for increased allergic sensitization in treated animals. Increased concentrations of heavy metals have been found in the body tissues (including lungs) of humans and other mammals living in areas with elevated metal-containing soils.
The body in response to acute injury, infection, or other inflammatory stimuli releases C-reactive protein (CRP) and cytokines. This response is called the acute phase reaction. Acute phase proteins are a class of proteins that are synthesized in the liver in response to inflammation. C-reactive protein is a special type of protein produced by the liver that is only present during episodes of acute inflammation. CRP is therefore a marker of inflammation. The most important role of CRP is its interaction with the complement system, which is one of the body's immunologic defense mechanisms.
Cytokines are small protein molecules that are the core of communication between immune system cells, and even between immune system cells and cells belonging to other tissue types. They are actively secreted by immune cells as well as other cell types. Their action is often local, but sometimes can have global effects on the whole body. Cytokines act by binding to their cell-specific receptors. These receptors are located in the cell membrane and each allows a distinct signal cascade to start in the cell, which eventually will leads to biochemical and phenotypical changes in the target cell.
It has recently been discovered that CRP also plays a role in heart disease. Atheromatous plaques, characterized by thickening and fatty degeneration of the inner coat in diseased arteries, typically contain inflammatory cells. Rupture of atheromatous plaque is thought to be the mechanism for acute myocardial infarction and acute coronary syndrome. The most common site of plaque rupture appears to be the shoulder region where inflammatory cells are most prominent. Thus the release of acute phase reactants as a response to inflammation have been proposed as a potential marker of an “unstable” atheromatous plaque and underlying atherosclerosis, the progressive narrowing and hardening of the arteries over time.
The amount of CRP produced by the body varies from person to person, and this is affected by an individual's genetic makeup. Higher CRP levels tend to be found in individuals who smoke, have high blood pressure, are overweight and don't exercise, whereas lean, athletic individuals tend to have lower CRP levels.
The toxicological consequences of inhaled particles on the cardiovascular system are also under increased investigation. The studies suggest that pathophysiological changes in cardiac function, such as heart rate variability, post-myocardial infarction; increased atherosclerosis plaque formation and/or blood coagulation could be linked to inhaled protein and other toxins found in respirable metal-associated particles.
What is needed are improved methods for improving indoor air quality such as in control of particulates in indoor air and reduction in allergen exposure by humans, adults and children, and animals.